Technical Field
The present invention relates to a rotary electric machine for a vehicle, the machine being installed in a passenger car, a truck or the like.
Related Art
Conventionally, a drive circuit is known which includes a protection circuit which logically detects overheat and over current of a power transistor to limit the operation thereof (for example, refer to JP-A-7-84655). This protection circuit prohibits the power transistor from being turned on when overheat or over current of the power transistor is detected which drives a load connected to the drive circuit.
According to the configuration of JP-A-7-84655, when an abnormal condition occurs, the power transistor is turned off to stop supplying current from the power transistor to the load. However, even if the protection circuit of JP-A-7-84655 is applied to the power transistor, which is included in a power converter of the rotary electric machine for a vehicle, current flows through a parasitic diode when the power transistor is turned off. Hence, when a ground terminal is disconnected, the current flowing through the parasitic diode can flow to a control circuit and to another electric load through the control circuit. In particular, when a 48V high-voltage battery is charged from a power system circuit, and a control system circuit is operated by being connected to a 12V low-voltage battery, current is reliably prevented from flowing from the power system circuit to the control system circuit even when the ground terminal is disconnected.
In addition, conventionally, an electronic circuit such as an in-vehicle AC regulator is known which maintains output control in a stable condition by prohibiting an output driver circuit and an output switching element from being driven when disconnection of a ground terminal is detected (for example, refer to Japanese Patent No. 2504586). This electronic circuit stops the control when the ground terminal is disconnected to prevent the output control from being disabled.
However, the function of the electronic circuit of Japanese Patent No. 2504586 cannot be applied to a case where one ground terminal is provided for the whole electronic circuit, and a plurality of ground terminals are individually grounded, and when one of the ground terminals is disconnected. For example, when assuming that a power ground terminal, which is connected to a power converter forming an inverter of a rotary electric machine for a vehicle, and a control ground terminal, which is connected to a controller controlling the power converter, are individually grounded, and the power ground terminal is disconnected, disconnection of the power ground terminal cannot be detected, and elements connected to the power ground terminal cannot be protected.
In addition, conventionally, an abnormality determination apparatus of an electric power unit is known which detects current and voltage of a battery to determine an open fault of the battery (for example, refer to Japanese Patent No. 4501873). This abnormality determination apparatus determines an open fault of the battery when the variation amount of voltage detected by a voltage sensor is larger, and the variation amount of current detected by a current sensor is smaller.
The abnormality determination apparatus of Japanese Patent No. 4501873 determines presence or absence of an open fault of the battery based on a relationship between the voltage and the current of the battery. Hence, a current sensor is required which detects a current flowing through a portion to be an object of the determination of an open fault, thereby complicating the configuration of the abnormality determination apparatus. For example, considering that disconnection of a control ground terminal is detected which grounds a control system circuit of the rotary electric machine for a vehicle, it is difficult to provide a current sensor for detecting the disconnection of the control ground terminal (open fault) because the space for installing the rotary electric machine is limited due to the requirement for miniaturization. In addition, since the amount of current flowing to the control system circuit is relatively small, it is difficult to accurately determine disconnection of the ground terminal based on the relationship between the current and the voltage.